Spark-ignited vehicles may use intake manifold vacuum to provide brake boost or power assist. Engine downsizing reduces the ability of these engines to provide brake booster vacuum. One existing solution is to add a vacuum pump, however the vacuum pump leads to parasitic fuel economy losses and increases overall vehicle cost.
In one approach described in U.S. Pat. No. 7,610,140, a vehicle ejector system has an ejector, a state change device that causes the ejector to function or stop functioning, and a control device that controls the state change device (Summary). “Furthermore . . . the control device may include a control prohibition portion that prohibits the control device from controlling the state change device so as to cause the ejector to function if water temperature of a cooling water of the internal combustion engine is less than or equal to a predetermined temperature” (col. 4 ll. 8-13).
The inventors herein recognize various issues with the above described approaches. During cold start, engine conditions (such as high manifold air pressure and low barometric pressure due to low temperature and/or high altitude) may limit the available vacuum for various engine systems, such as the brake booster. In downsized engines including a supercharger and/or turbocharger, boosting may further reduce the conditions under which brake vacuum is available. Further, as a range of cylinder pressures increase, so does a range of intake passage pressures increase. Intake systems including a single fixed geometry aspirator may function inefficiently or not at all at some pressures of the increased pressure range.
Consequently, methods, systems and devices for a vacuum aspirator included in an intake system are described. In a first example, an intake system includes an intake passage including a compressor, a throttle and an intake manifold, and an aspirator having a motive inlet communicating with the intake passage intermediate to the compressor and the throttle and the aspirator having an entraining inlet communicating with a vacuum reservoir via a first check valve, the reservoir different from the intake manifold, and the first check valve limiting flow from the intake passage to the vacuum reservoir.
In a second example, an intake system includes, a throttle, the throttle including a first inlet, a second inlet, and a plate, the plate located intermediate the first inlet and the outlet, the second inlet located intermediate to the throttle plate and the first inlet, the throttle positioned in an intake passage, and an aspirator having a motive inlet in communication with the intake passage, the aspirator having an outlet in communication with the second inlet of the throttle, the aspirator having an entraining inlet in communication with a vacuum reservoir via a first check valve, the first check valve limiting flow from the second inlet to the vacuum reservoir.
In a third example, an intake system having a plurality of vacuum boosters for a vacuum reservoir, includes a first aspirator having a first motive inlet, first entraining inlet, and first outlet, the first motive inlet in communication with an intake passage adjacent a high pressure outlet of a compressor, and a second aspirator having a second motive inlet, second entraining inlet, second outlet, and second check valve, where either the second outlet is in communication with the first entraining inlet or the second motive inlet is in communication with the first outlet, and the second entraining inlet in communication with a vacuum reservoir via the second check valve, the second check valve limiting from the second entraining inlet to the vacuum reservoir.
One advantage of the above examples is that excess compressor pressure and flow is used to generate vacuum. In this way, downsized engines including a turbocharger or supercharger may generate vacuum, even during cold start. Further, an example throttle including a first inlet and a second inlet may control flow through an example aspirator, as well as flow to an example manifold not from the aspirator, simplifying an intake system configuration. In examples including a plurality of aspirators one of the plurality may be configured for high flow and another may be configured for low flow, increasing an intake system's efficiency at generating vacuum over a wide pressure range.
It will be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description, which follows. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined by the claims that follow the detailed description. Further, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.